<html xmlns="http://www.w3.org/1999/xhtml" xmlns:math="http://www.w3.org/1998/Math/MathML">
<head>
<script>

function boom()
{
  var mtd1 = document.getElementById("mtd1");
  var mtd2 = document.getElementById("mtd2");
  var newSpan = document.createElementNS("http://www.w3.org/1999/xhtml", "span");

  mtd1.appendChild(newSpan);
  mtd1.removeAttribute("columnspan");
  mtd2.setAttribute("columnspan", 0);
}

</script>
</head>

<body onload="boom();">
<math:mtd id="mtd1" columnspan="5" /><math:mtd id="mtd2" />
</body>
</html>
